* support user-defined quant and preprocess

* add matmtl_v2 to amp list

* support dygraph

Fix a bug that used in PaddleGAN model which used `isinstance` in a for loop

* adapt pad const

* fix comment and rm fluid import

* rm stdout

* fix note

* fix output dtyp inconsistent with input

* refine code

fix the gradient bug for the topk v2 

* add WeightedRandomSampler. test=develop

* Add checkpoint to quantize

* Change bfloat16 option

* add mkldnn inplace op version test

* update mkldnn_inplace fuse pass

* update the inplace test

* fix test_multinomial

* fix test_multinomial add 0 prob

* DataLoader support not auto collate batch. test=develop

PaddleSeg uses tuple as parameter of transpose in dygraph code:
https://github.com/PaddlePaddle/PaddleSeg/blob/release/v0.7.0/dygraph/paddleseg/models/danet.py#L152

However, in dy2stat, static code doesn't support the perm as a tuple. This PR fixed it.

* Fix gradients with ignore_idx in softmax_with_cross_entropy.
test=develop

* Fix gradients with ignore_idx in softmax_with_cross_entropy on cpu.
Remove softmax_with_cross_entropy from op_threshold_white_list.
test=develop

* Fix test_softmax_cross_entropy_op.py.
test=develop

I found the unittest failed due to batch size. Maybe the reason is that our CI machine has limited memory. I decreased the batch size.

* update, test=develop

this is a preemptive measure, the unit test was failing occasionally with
cudnn internal error

* add onnx export module, test=develop

* add unit test for paddle.onnx.export

* adjust api & doc

* fix some typo

also fix `no_grad` alias

* skip_layernorm_op done

* add unittest

* slice op convertor support trt < 6

* skip_layernorm only work in ernie

As the title

1. Remove 'fluid';
2. Variable -> Tensor

APIs:
 sum, convert_call, convert_ifelse,
 convert_logical_and, convert_logical_or, convert_logical_not

Modify ProgramTranslator and TracedLayer Doc for API 2.0

Remove "fluid", "variable" in 2.0 API doc

As the title

* fix ut exec timeout notest,test=kunlun

* fix error for executing ut timeout,test=document_fix

* modified timeout value on windows

* fix some error

* exec ut no more than 15s 2

* fix for ut test_inplace_addto_strategy timeout